Delivery of gaseous fuels such as LPG or CNG to internal combustion engines presents a whole different set of problems than those encountered with liquid fuels, such as gasoline. For one thing, gaseous fuels are of different densities than the air with which they are to mixed to form a combustible mixture, causing the gaseous fuel to stratify and remain in boundary layers, separated from the air along the intake track. The stratification leaves clusters of fuel molecules which can be only partially burned, resulting in a loss of potential power from the engine, excessive fuel consumption and excess hydrocarbons and other undesirable pollutants to be present in the exhaust.
Furthermore, to achieve an energy or BTU output similar to that of gasoline, a significantly greater volume of the gaseous fuel is required, such as for exampie, two to three times more. Dealing with greater volumes of fuel further increases the difficulty of achieving a proper mixing of the fuel and the air, thus increasing the probability of undesirable exhaust emissions.
Mixing devices for mixing gaseous fuels and air are known, but most of such devices merely substitute a mixing chamber having a throttle controlled butterfly valve for the conventional carburetor in a liquid fuel type of engine. Such a device with upstream fuel delivery is described in U.S. Pat. No. 4,765,303. Contrary to the present invention, where the pressure drop across a diametrically disposed fuel delivery. bar is primarily responsible for creating the fuel flow into the air intake tube, the '303 device depends upon throttling a fuel valve in response to negative pressure signals from a Venturi in the main fuel/air stream.
U.S. Pat. No. 4,370,969 discloses a propane gas feed system wherein controlled and measured quantities of gas are pre-mixed with air and then fed to a carburetor. An air cut off screen is used to control the air/fuel ratio relative to a changeover from propane to gasoline.
In U.S. Pat. No. 4,632,083 a control unit senses operating pressures along the intake pipe system in the injection zone and in the zone downstream of the throttle valve in order to control an expander unit which feeds the gaseous fuel to a volumetric measuring device at a pressure equal to the sum of the absolute values of the two pressures at the pressure measuring points.
U.S. Pat. No. 4,526,155 discloses a pressure regulating system for preparing the mixture of gas and air for an internal combustion engine.
In other gaseous fuel management devices, for a particular engine icad requirement, gaseous fuel is drawn into the mixing chamber through a fuel valve which is responsive to the engine intake manifold pressure being sensed by a spring loaded diaphragm. One such arrangement is disclosed in U.S. Pat. No. 4,694,811. In some devices, a separate air valve is also supplied in an effort to achieve the correct fuel-air mixture for best combustion results and lowest undesirable emissions. Such a device is shown in U.S. Pat. No. 2,311,315.
One of the significant problems with arrangements which depend upon the suction created by the intake manifold pressure for establishing fuel flow and fuel control is the exacerbation of the exhaust emissions problem during the period immediately following a quick closing of the throttle valve for deceleration. When the throttle valve is suddenly closed, or its opening is substantially reduced, the air flow into the intake manifold is abruptly reduced, creating a high vacuum in the manifold which continues to suck or induce the delivery of higher levels of fuel than is required for the reduced amount of air being admitted into the intake manifold with the reduced throttle opening. The resultant excessively rich mixture is not completely burned and highly undesirable exhaust emissions are produced.
It is thus the primary object of the present invention to provide apparatus for improved blending of air and gaseous fuels prior to introduction of the mixture to the combustion chambers of an internal combustion engine so as to reduce fuel consumption and give superior power performance.
A further object of the invention is to increase combustion efficiency in a gaseous fuel internal combustion engine and significantly decrease carbon monoxide emissions therefrom.
Another object of the invention is to provide gaseous fuel/air mixing apparatus which will be efficient enough to permit the internal combustion engine to operate on less fuel than is the case with prior art gaseous fuel engines.
A still further object of the invention is to provide fuel management apparatus which is immediately responsive to deceleration throttle commands and will not provide excessively rich fuel/air ratios and excessive emissions in the period of time immediately following a quick closing of the throttle.
Other and still further objects, features and advantages of the invention will become apparent from a reading of the following detailed description of a preferred form of the invention taken in conjunction with the accompanying drawings.